DSM/Tape Catalog User's Guide

Tape File Concepts

DSM/Tape Catalog User’s Guide — 520233-008

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Absolute Generations

Every generation of a tape file entry has an absolute generation number, which is the

number it was given when the entry was created (1, 2, 3, and so on). When you want a

particular generation of a tape file, you can use an absolute generation number in the

GEN attribute of the TAPECATALOG DEFINE.

Example

For example, assume a special report is required from the data in generation 3 of

MASTER_ACCT. So far the file catalog contains five generations of MASTER_ACCT:

The application uses this DEFINE to retrieve tape T00136 and generation 3 of

MASTER_ACCT:

6>ADD DEFINE =REPORT_IN, CLASS TAPECATALOG,&

6>& USE IN,&

6>& FILEID MASTER_ACCT,&

6>& GEN 3

Requesting a tape file by absolute generation number works only when that generation

exists in the catalog. If the tape file entry is missing because it expired, was manually

deleted, or never existed, the request fails.

Relative Generations

Another way to specify a tape file generation is with a relative generation number.

These numbers are always negative numbers referring to the relative position of a tape

file entry within a group of generations. The latest or most current entry in the group is 

-1, the next latest one is -2, and so on, down to the oldest entry in the group. Unlike

absolute generation numbers, these numbers are not stored in the t

ape file entry. Even

though these examples imply that the numbers are stored in the entries, they describe

how DSM/TC indexes through the entries to find the one you want.

Requesting a tape file by its relative generation number works with whatever t

ape file

entries exist in a generation group.

Tape File Name Tape Name Generation Creation Date

MASTER_ACCT T00045 1 February 3

MASTER_ACCT T00102 2 February 10

MASTER_ACCT T00136 3 February 17

MASTER_ACCT T00155 4 February 24

MASTER_ACCT T00188 5 March 2